Changing Wordpress Permalinks causes 500 Internal Server Error

When I choose the permalink option "Plain," my site functions as expected.

When I choose anything else, the links on my site change, but attempting to navigate to either the new (/$category/$postname) or the old (?post_id=123) links throws a 500 error.

I enabled Wordpress debug logs but nothing is showing up in the file.

The contents of my .htaccess file (in my subdomain's public_html directory) are

<ifmodule mod_rewrite.c="">
RewriteEngine on
RewriteCond %{HTTP_HOST} ^(www.)?extinction-resilience.org$
RewriteCond %{REQUEST_URI} !^/wordpress/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /wordpress/$1
RewriteCond %{HTTP_HOST} ^(www.)?extinction-resilience.org$
RewriteRule ^(/)?$ wordpress/index.php [L] 
</ifmodule>
# BEGIN WordPress
<ifmodule mod_rewrite.c="">
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</ifmodule>

# END WordPress

Folder structure:

/my main site/subdomain/public_html/wordpress/wordpress installation

I set up a rule in the Wordpress settings to remove the /wordpress from the URL and that works fine.